Engines, especially diesel engines, operate most efficiently when the fuel delivered to the engines is maintained within a desired temperature range. The low end of the desired range is above low fuel temperatures at which fuel may thicken (wax). The high end of the desired temperature range is below high fuel temperatures at which engine power output deteriorates.
Fuel waxing is apt to occur during cold weather, when the fuel tank of a vehicle is exposed to the environment. Under such conditions, fuel in the fuel tank may thicken. Such thickened fuel may clog the engine fuel inlet lines. The clogging may result in compromised engine performance or engine shutdown. The small fuel lines of electronic fuel injectors prevalent today are especially vulnerable to such clogging.
Engine power output may deteriorate when the fuel being delivered to the engine becomes excessively warm. For example, the power output of diesel engines may decline by one horsepower for every 10.degree. F. of fuel temperature over 100.degree. F. Moreover, over-heated fuel may be detrimental when fuel is used to cool engine equipment, such as in a heat exchange relationship with electronic engine controls. Such over-heated fuel may inadequately cool the engine equipment, resulting in a reduced service life for that equipment.
Fuel tends to become excessively heated when stored in a vehicle fuel tank during very hot weather. Fuel also becomes overheated when used to cool engine equipment. As much as 80% of the fuel directed from the fuel tank to the engine is returned unused (uncombusted) by the engine and is used for equipment cooling as the fuel is returned to the fuel tank. The fuel picks up heat from equipment being cooled, which tends to increase the temperature of the fuel.
Therefore, it is desirable to maintain the fuel delivered from the fuel tank within a temperature range that minimizes problems associated with waxing, degraded power output and inadequate engine equipment cooling.
One prior art approach uses radiators to cool the fuel. However, radiators tend to be expensive and prone to damage. Another approach uses a two fuel tank system to address the problem of hot fuel that is recycled from the engine. The first tank receives the hot recycled fuel for storage and gradual cooling, and the other tank receives cooled fuel from the first tank for delivery to the engine. This approach has a drawback in that, on very warm days, the fuel in the tanks may not cool adequately. Moreover, when the fuel level in the tanks is low, the hot fuel may not be stored in the cooling tank long enough for adequate cooling. Furthermore, these approaches do not address the problem of fuel that is too cold.
Wolf U.S. Pat. No. 4,748,968 discloses a fuel heating device in which relatively hot engine coolant circulates around a fuel tank suction tube to warm fuel taken from the fuel tank. The Wolf device requires a coolant fluid circuit extending between the cooling system and the fuel tank.
Stone U.S. Pat. No. 5,042,447 discloses a thermostatically controlled fuel heater and cooler. The Stone device monitors the fuel temperature and appropriately directs the fuel into a fuel heating heat exchanger utilizing relatively hot engine coolant for heating, or a fuel cooling heat exchanger utilizing a refrigerant for cooling. The coolant and refrigerant of the Stone device circulate through lines which are lifted into the engine cooling system, and the air conditioning system, respectively. Consequently, the Stone device adds to the complexity of these systems.
A need exists for an improved apparatus for temperature control of fuel which overcomes these and other disadvantages of the prior art.